The invention pertains to a flow medium for distributing a resin in resin transfer molding processes.
Vacuum assisted resin transfer molding (VARTM) is a process for manufacturing composite structures using a hard surface mold and a thin flexible membrane that enclose the components of the composite structure. One or more fiber reinforcement layers, for example of glass, carbon and/or aramid fibers, are layered in the hard surface mold and a thin flexible membrane or a second matching hard surface mold is put on top of the fiber reinforcement layers to close off the fiber reinforcement layers from the surrounding atmosphere. In addition, one or more core layers may be included in the fiber reinforcement layers, such as for example closed-cell foam, balsa or sealed honeycomb layers. A vacuum is applied through the membrane or mold to help draw resin into the sealed mold and the resin infiltrates into the fiber reinforcement layers. When the resin is cured, the composite structure can be removed from the mold.
In the VARTM process, the resin remains in a closed system and the chance for volatile off-gassing is minimized. By comparison, an open mold (spray up) process is open to the surrounding atmosphere and resin is delivered to the components directly.
In a closed molding system, speed and volume of resin delivery is critical to efficient and effective molding of composite structures. Resins generally have a limited pot life and the quality of the composite structure can suffer from poor quality resin when long times are needed to fill the mold with resin. The resin generally contains activating agents to initiate curing of the resin as the resin flows into the mold and infiltrates the fiber reinforcement layers. There is a delicate balance between curing the resin as quickly as possible to increase productivity and the ability to deliver the resin to the desired areas in the desired volume and before curing of the resin has progressed too far, which limits the flow of the (partially) cured resin.
As composite parts become longer, thicker and more complex, traditional means of resin delivery are not sufficient for delivery of the required resin volume in a timely manner. Wind blades, for example, are becoming larger and longer, and the ability to deliver resin quickly along the entire length of a blade mold is highly desirable. Ship hulls are becoming a more complex mixture of thick and thin areas providing increased challenges for the producer to supply the desired resin volume to the thick and thin areas.
A flow medium can be applied between the fiber reinforcement layers and the thin flexible membrane to improve the resin distribution in the mold in the VARTM process.
US 2003/0211194 applies a high permeability layer to yield an optimum flow front, the high permeability layer being either a felt-like material or a rubber or plastic fluid-impervious layer with non-directional protrusions on the side facing the fiber reinforcement layers. Such felt-like material or rubber or plastic fluid-impervious layer with non-directional protrusions do not provide sufficiently fast resin delivery in large composite parts.
US 2003/0148090 applies a flow channel medium for the passage of resin, the flow channel medium being a plastic mesh with large open volume. Such a plastic mesh with large open volume does not provide sufficient volume flow of resin in long composite parts.
WO 2007/098769 A1 discloses the use of inlet channels between a layer of fibrous material and a vacuum bag in a vacuum infusion process. The layer of fibrous material acts as flow medium, but does not always provide sufficiently fast resin delivery in large composite parts.
WO 2009/115878 discloses an autoclave method for producing fiber composite components wherein a sprue profile rests on a flat flow promotor comprising a woven fabric or knitted fabric. The flat flow promotor acts as flow medium, but does not always provide sufficiently fast resin delivery in large composite parts.
DE 10203975 C1 discloses a process for injection molding of fiber composites wherein an inlet channel is placed on top of a distribution fabric. The distribution fabric acts as flow medium, but does not always provide sufficiently fast resin delivery.
Hoebergen et al. disclose in Composites—Vacuum Infusion (ASM Handbook—Composites, pages 501-511, ISBN 978-0-87170-703-1) a process for vacuum infusion wherein resin distribution channels are placed directly on the fiber reinforcement layer or on a flow layer such as a nonwoven, a coarse weave or welded net. The flow layer acts as flow medium, but does not always provide sufficiently fast resin delivery, especially in large composite parts.
EP 2374605 A1 discloses an elastomeric resin flow channel placed on a mold surface, the flow channel being covered a fibrous layer, which in turn in covered by a membrane. The flow channel is placed directly on the fiber reinforcement layer. The fibrous layer is designed to provide a bondable surface for releasably bonding a reusable membrane on the top and side surfaces of the flow channel. The flow channel does not always provide optimal distribution of resin over the surface to be impregnated.
US 2008/0079193 A1 discloses the use of a resin distribution tube above and away from the preform to avoid direct contact of the resin distribution tube to the preform in order to eliminate deformations on the resin infused composite parts. By placing the resin distribution tube above and away from the preform, the speed of delivery and distribution of resin to the fiber reinforcement layer is not optimal.